1. Field of the Invention
The present invention relates to specific modified colorants and inkjet ink compositions comprising these modified colorants.
2. Description of the Related Art
The surface of pigments contains a variety of different functional groups, and the types of groups present depend on the specific class of pigment. Several methods have been developed for grafting materials and, in particular, polymers to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods which rely on the inherent functionality of a pigment's surface cannot be applied generally because not all pigments have the same specific functional groups.
Methods for the preparation of modified pigment products have also been developed which can provide a pigment with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt.
Other methods to prepare modified pigments, including those having attached polymeric groups, have also been described. For example, PCT Publication No. WO 01/51566 discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Ink compositions, including inkjet inks, containing these pigments are also described. In addition, U.S. Pat. Nos. 5,672,198, 5,922,118, 6,042,643, and 6,641,656 disclose modified pigments having various attached groups, including phosphonic acid groups. Also, U.S. Pat. Nos. 6,328,894, 6,398,858, 6,436,178, 6,494,943, and 6,506,245 disclose modified pigments having various attached groups, including aryl polycarboxylic acid groups, including 1,2,3-benzene tricarboxylic acid groups. Compositions comprising these modified pigments, including inkjet ink compositions, are also shown. Also, polymer coated carbon products and methods for their preparation are described in U.S. Pat. No. 6,458,458.
While these methods provide modified pigments having attached groups, there remains a need for modified pigments having improved performance properties in compositions such as inkjet inks, thereby providing advantageous alternatives to previous modified pigments.